ALICE rf project meeting

Urban and Civil

Nov 15, 2013 (4 years and 5 months ago)

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1

ALICE rf project meeting

Kai Hock, Cockcroft / Liverpool

19 May 2008

2

Status

Aug
-

Worked through Wiedemann’s chapter, Perry Wilson’s report on rf system

basics, 4GLS

Feb 08: ALICE rf control

new phase

Mar 08: ALICE

intro to rf system (Andy)

Apr 08:

Contacted, received paper, suggestions from Tom Powers

Looking up references: rf feedback, energy recovery theory, …

Started learning rf control hardware, set up by Andy

May 08

Simulation on klystron power

with energy recovery ?

Set up stretched wire experiments ?

3

RF system theory

Feedback control

experiments

Stefan Simrock’s LLRF lectures

Papers on ELBE rf system

Sakanaka’s ERL07 paper (4GLS simulation)

Energy recovery linac

Thomas Schilcher’s PhD thesis (microphonics, Lorentz detuning)

Tom Power’s paper

4

Deciphering Tom’s paper

Why / how does energy recovery happen?

What are r/Q,

Q
L
, Q
0
,

,

f
S
,

B
, …
?

How does the klystron power equation come about?

What are microphonics, Lorentz detuning, ponderomotive
effects, vector sum, … ?

Why are we interested in detuning? What are mechanical
tuners?

Why is detuning measured by the Klystron
-
cavity phase
difference?

When Q
L

is optimized, what exactly is minimised or
maximised? The klystron power?

Why is incomplete energy recovery needed? How does

What are page 2, page 3, page 4 and page 5 about?

Questions from a complete beginner

5

Why Energy Recovery

“ … the beam
-
induced voltage in a cavity is the same
whether or not a generator voltage component is present.”

(Wilson 1991,

The beam induced voltage is always negative.

Therefore, if a bunch enters at the opposite phase
of the cavity field, it will increase the amplitude of
the field.

This gives energy to the cavity.

(Sakanaka ERL07)

6

Shunt Impedance

(Wiedemann 2003)

A full calculation from Maxwell’s equations for pillbox cavity:

7

Many equations come from this !

(Wiedemann 2003)

8

r/Q,

Q
L
, Q
0
,

,

B
, …

(Wiedemann 2003)

This
models

the behaviour of

the cavity voltages.

Mostly using

equations from

simple harmonic

oscillator.

9

How the beam affects the cavity voltage

All voltages defined along the axis of cavity (beam path):

generator (klystron) voltage V
g

beam induced voltage V
b

and resultant cavity voltage V
c

Assuming all sinusoidal, they can be related by a phasor diagram.

(Wilson 1991)

10

The klystron power equation

2 2
2
0 0
(1 )
1 cos tan sin
4
c L L
g b b
L c c
V I R I R
P
R V V

 

 
   

 
   
 
   
   
 
 
r/Q,

Q
L
, Q
0
,

, … are measured

by fitting to the equivalent circuit model

The klystron power can be calculated

from these parameters using the model.

Merminga (2001) explains how to get this:

Steps are easy once we have worked from

Wiedemann and Wilson.

The main equation

in Tom’s paper

11

Energy recovery calculations

ERL Injector and Linac:

f
m
=25 Hz, Q
0
=1x10
10

, f
0
=1300 MHz, I
0
=100 mA, V
c
=20 MV/m, L=1.04 m,
R
a
/Q
0
=1036

ohms per cavity

ERL linac: Resultant beam current, I
tot

= 0 mA (energy recovery)

and

opt
=385

Q
L
=2.6x10
7

P
g

= 4 kW per cavity.

ERL Injector: I
0
=100 mA and

opt
= 5x10
4

!

Q
L
= 2x10
5

P
g

= 2.08 MW
per cavity!

Note: I
0
V
a

= 2.08 MW

Nice examples from Merminga (2001)

12

Microphonics, Lorentz Force, Vector Sum

(Schilcher 1998)

Revelation !

13

What exactly is being optimized?

(Liepe PAC05)

The klystron power, of course !

14

Ponderomotive force

15

Page 2 of Tom’s paper

One bunch at a time?

10
o

165
o

1
st

pass

2
nd

pass

I
B

?

Shall try to do this next

16

Experiments

References on Feedback control

Stefan Simrock’s LLRF lectures

Papers on ELBE rf system

Andy’s Rossendorf control unit

Connect control system to standalone cavity

Stretched wire measurements with short pulses

Ideas for experiments